ABSTRACT Even with successful viral control, HIV-infected individuals exhibit co-morbidities associated with older age, including osteoporosis, stroke, dementia, and cancer. In aviremic HIV+ individuals and the general geriatric population, age-associated diseases and mortality correlate with plasma markers of inflammation and intestinal permeability. The gut is a major reservoir of latently HIV-infected cells, and HIV enteropathy, defined as pathologic processes in the small intestine and colon, is a hallmark of HIV infection. Our preliminary data implicate gamma delta (??? T cells as an inflammatory driver in ART-suppressed HIV infection and with normal aging. ?? T cells are a non-conventional T cell lineage that comprise ?10% of circulating T cells yet are found in considerably higher proportions in the epithelium of the intestine. Also, there is evidence that this unique T cell population regulates intestinal barrier function during normal conditions, and that ?? T pro-inflammatory activity causes damage at epithelial sites and to epithelial barriers. Therefore, we hypothesize that with virally suppressed HIV infection and with normal aging, gastrointestinal ????T cells are stimulated via directly harboring HIV and/or exposure to inflammatory factors and this aberrant activation leads to breakdown of tight junctions of the intestinal epithelial barrier, causing increased release of microbial products and inflammatory ?? T cells into the circulation. Further, we predict that aged ?? T cells exhibit functional profiles skewed towards inflammatory cytokines/cytotoxicity in response to either direct HIV infection and/or stimulatory factors. In this application, we propose to test these hypotheses using advanced and innovative approaches, including 25-color flow cytometry, 31-color imaging mass cytometry of recto-sigmoid biopsies, 19- and 33-plex analyses of plasma and cell culture supernatants, respectively, and multiple algorithms for multivariate analysis of collected datasets. Our bioinformatic data analysis plan will enable identifying novel ?? T cell subsets and parsing the differential impacts of age with and without HIV infection. In Aim 1 we will perform a cross-sectional study of our HIV and Aging cohort to determine the links between circulating ?? T cell subsets, plasma inflammatory and intestinal permeability markers, and intestinal architecture and cellular composition. In Aim 2 we will determine the temporal links between ?? T cell subsets, plasma markers, and the onset and/or progression of geriatric outcomes via a longitudinal study of older subjects with and without ART-suppressed HIV. In Aim 3, we will perform in vitro assays to determine how age and HIV infection impact ?? T cell functions, including the capacity to breakdown intestinal epithelial cell monolayers. We predict that our proposed experiments will identify the biological mechanisms that drive the increased systemic inflammation and age-associated comorbidities in both aviremic HIV+ individuals and the general geriatric population; such insight could lead to the development of novel therapeutics to reduce ?inflamm-aging?-associated diseases and deaths.